In recent years, in the fields of automobiles, office machines and tools, and electrical products, efforts are being made to convert parts especially made of sheet metal to those of resinous sheet for the purpose of lessening weight, lightening energy consumption, and reducing cost. As the result, such heat-resistant and impact-resistant resins such as alloys of polycarbonate and ABS resin and modified PPE have already found utility in various parts.
The styrene-acrylonitrile copolymer (AS resin) is a transparent thermoplastic resin excelling in resistance to chemicals and possessing high mechanical strength and exhibiting highly satisfactory compatibility as with the ABS resin and, therefore, has found extensive utility as a molding material. The resin composition using this copolymer, owing to its inferior resistance to heat, finds greatly limited utility in industrial applications.
As a way of improving the AS resin's resistance to heat, the incorporation of an .alpha.-methyl styrene unit and a maleic anhydride unit in the molecular chain has been known to the art, for example. In this case, however, the produced resin is not practicable because it is decomposed at high temperatures.
This resin has another disadvantage that the blow molding technique cannot be adopted for the manufacture of a large shaped article of the resin because the phenomenon of drawdown due to the pyrolytic property of .alpha.-methyl styrene occurs heavily.
As a way of alleviating the effect of the drawback of .alpha.-methyl styrene mentioned above, the idea of improving the AS resin's resistance to heat by having a N allyl maleimide unit into the molecular chain of the resin has been proposed (U.S Pat. No. 3,652,726, U.S. Pat. No. 3,766,142, Japanese Patent Publication No. 50,357/1987, and Japanese Patent Publication No. 34,961/1989).
The terpolymer of styrene, acrylonitrile, and N allyl maleimide obtained by this method, however, is not desirable because it has a markedly large composition distribution as a polymer, betrays conspicuous deficiency in such physical properties as resistance to heat and mechanical strength, and manifests slightly inferior transparency and, therefore, finds only limited utility in industrial applciations.
Further, the resin composition using this terpolymer has the problem of insufficient improvement in mechanical strength and resistance to heat distortion.
As a way of uniformizing the composition distribution of the terpolymer, it is known that the method of continuous solution polymerization can be advantageously resorted to. A method for producing the aforementioned terpolymer by the technique of continuous solution polymerization is disclosed in Japanese Patent Application Disclosure No. 276,807/1986. In the case of this method, though the produced terpolymer acquires uniform composition distribution as a polymer, it has no sufficiently improved resistance to heat. When phenyl maleimide is supplied in a large amount to the polymerization vessel for the purpose of heightening the resistance to heat, the reaction solution containing a large amount of maleimide induces a side reaction in a volatile component removing device and consequently gives rise to a fairly large amount of oligomer and the phenyl maleimide eventually persists in the produced terpolymer.
When the amount of the phenyl maleimide monomer persisting in the terpolymer exceeds 50 ppm, the monomer exudes from the terpolymer and passes into a neighboring substance such as a foodstuff and consequently entails a problem of toxicity. When the resin is used for molding a shaped article, the resin assumes a conspicuous color, discharges a viscous exudate, suffers from deficiency in resistance to heat, and finds only limited utility in industrial application.
In the conventional technique, when the volatile component removing device is operated under the conditions of high temperature and high vacuum for the purpose of decreasing the residual phenyl maleimide content, the operation of the device gives rise to a large amount of oligomer such that the produced terpolymer suffers from lack of uniform composition distribution as a polymer and the resin succumbs to thermal decomposition and thermal coloration.
The present inventors have continued a diligent study in search of a copolymer which concurrently satisfies the heretofore unattainable conditions of offering high resistance to heat, exhibiting a uniform composition distribution as a copolymer, and having a residual phenyl maleimide content of not more than 50 ppm and, what is more, excels in transparency. This invention has been perfected as the result.
The inventors have further continued this diligent study with a view to developing a thermoplastic resin having the copolymer as one component thereof and excelling in resistance to impact and resistance to heat, to find that a thermoplastic resin composition obtained by combining the aforementioned terpolymer and a specific thermoplastic copolymer in a specific ratio and a composite material obtained by incorporating glass fibers, glass flakes, or polycarbonate resin in the aforementioned terpolymer or composition satisfy the conditions mentioned above. This invention has been perfected as the result.